Basic Construction Training Manual (Civil)

8/10/2019 Basic Construction Training Manual (Civil)

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Basic Construction Training Manualfor Trainers

Heini Mller


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Basic Construction Training Manualfor Trainers

Heini Mller


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References of sketches

1. E lem entary course on B uilding C onstruction and M aterials SATA

2. B rick w ork M anual Lau rie B aker

3. B uilding C on struction M anual SKAT

4. Joints in M asonryM o du le M M 13

H abitat Po lytech, R ichm ar

Impessum

A utho r: H eini M ller

C opyright: S kat Fo undation, S t.G allen, Sw itzerland 20 04 , 1 st edition, 20 0 C op ies

C opyright w aiver: Perm ission is granted to use the m aterial foun d in this volum e for educationaland d evelopm ent purposes. A cknow ledgem en t is requested .

Layout: M artin Lng, A lex B ch i; Skat Foundation

SR CSw iss Red C rossP.O . B ox 26 99R ainm attstrasse 10C H -30 01 B ern, Sw itzerlandhttp://w w w .redcross.chem ail: iz@ redcross.ch

SEW ASelf Em ployed W om ens A ssociationSew a R eception C entreO pp. Lok M anya Tilak B aug, B hadraA hm edabad 3 80 0 01, Indiaem ail: sew a.m ahila@ w ilne ton line .ne t

Skat FoundationVadianstrasse 42C H -90 00 St. G allenSw itzerlandhttp://w w w .skat.chem ail: info@ skat.ch

Sw iss S olidarityB .P. 13 2R ue d es M arachers 8C H -1211 G enve 8Sw itzerlan dhttp://w w w .bo nh eu r.chem ail: info@ bonhe ur.ch


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Foreword

The d evastating earthquake of January 26 , 20 01 caused trem endo us d am age to the lives and

property o f the population living in the northern and northw estern districts o f G ujarat. In thew ake of this hum anitarian tragedy a large num ber of local, national and international organ isa-tions e ngag ed in relief and rehab ilitation operations.

A diverse range of strategies w as adop ted to m ee t the urge nt nee ds of the suffering p opu lationto rehab ilitate the ir lives and reco nstruct their house s. In line w ith its p rinciples, Sw iss R edC ross prom oted a process-oriented and com m unity-centred approach, taking into conside rationthe actual needs of the people an d the specific conditions of the area. A ccordingly, the ruralvillagers, especially w om en, w ere identified as a pro-active force building on their ow n strengthrather than becom ing passive recipients of external aid.

A fter a participatory assessm ent in three rem ote villages A ntarnesh, B aku tra and G adsai of

Patan district, Sw iss R ed C ross d ecided to contribute to the rehab ilitation of the lives of ninehund red fam ilies, throug h providing them w ith new , earthquake save houses, kitche ns, toiletsand w ater harvesting system s, called N aya G har (N ew housing). Th is infrastructure-focusedim prove m en t w as m ainly see n un de r the aspect of securing pe op les livelihoo d by creatingem ploym ent opportunities in the building sector.

The follow ing co m plem en tary organ isations w ere engage d in the Sw iss R ed C ross and Sw issS olidarity supported N aya G harProject:

n S E W A , (S elf-em ployed W om ens Association ) w ith its w ide ne tw ork of m ore than50 0000 m em be rs in G ujarat w as se lected as the m ain local project im plem en ting partne rorgan isation.

n D A (D eve lop m en t A lternatives), an Ind ia based N G O , in coo pe ration w ith S kat C on sultingfrom Sw itzerland, w ere selected to ensuring the practicab ility and quality o f theconstruction w ork.

Th e earthquake unfortunately p roved that local construction techn iques and skill did not preventhouses from collapsing during the incident. Th is clearly indicated the urgent need to im proveon b oth, co nstruction technologies an d e sp ecially on construction skill.

Fo r this reaso n the B asic C onstruction Training M anual for Trainers has been deve loped byS kat in close cooperation w ith field b ase d S E W A construction e ngineers to e nsure that theirne eds and exp ectation s are m et. Th is Training M anual is the sum m ary of basic p ractical con-struction know -how that is o f crucial im portance to transfer appropriate and new skills to localm asons, sup ervisors and S E W A m em be rs in b uilding earthq uake resistant ho use s. It w ill he lp

construction trainers to pass on relevant skills in constructing houses and im proving infrastruc-ture in a p ractical m anner, and offers a w ide range of essential inform ation.

B eside the Sw iss R ed C ross and S w iss S olidarity suppo rted N aya G har Project, this B asic C on -struction Training M an ual for Trainersw ill also se rve o ther S EW A construction related projects.A ll partners active ly involved in the creation an d ap plication of this Training M an ual hope thattrou gh it the ne w skills acquired by local m asons, supe rvisors and S E W A m em be rs w ill leadto an better building standard and quality, preventing further loss of lives and property in thisearthquake prone part of India.

Pe ter Epp lerProgram m e C oordinatorSw iss Red C ross


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General Introduction

W hen G ujarat has b een hit by the h orrifying e arthquake in January 20 01, international help

for the recon struction of houses an d creation of livelihoo d w as so on at hand and w arm lyw elcom ed by the needy one.

Th e concerned go vernm en t autho rities an d non -go vernm en tal organisation s launched re-construction activities w ith an astonish ing sw iftness. The resu lting focu s of constructionactivities in G ujarat w as dem and ing a hug e n um be r of skilled con struction m anpow er that w asreg rettably n ot alw ays easy at hand.

Th is Basic Construction Training Manual for Trainers is tailor m ad e for the specific cap acitybu ilding / training ne ed s o f S E W A for the earthq uake reconstruction prog ram m e that is,financed by the Sw iss S olidarity Fond and im plem en ted in partne rship w ith S w iss R ed C rossand techn ically coache d by Skat_consulting.

Th is m anual is sp ecifically focussing o n the practical im plem entation level and provides a w iderange of essential inform ation as w ell as d os an d do nts for traine rs to com m unicate to m asonsand supervisors during theoretical and on the job trainings. It also contains photos and ske tche s/ draw ings that add clarity to the context. Th ese photos and sketche s have b een collected fromvarious reference sources an d are therefore, not of uniform character in its present form .

Th is m anual is d ivided into five separate m odules. Module one exp lains the overall andessential parts of a building. Module two provide s inform ation about the qu ality b en chm arkand testing m etho ds o f bu ilding m aterials that are m ost com m on ly used in h ou sing construc-tion in G ujarat. Module three describes the skilled w orking principles for; M ortar, C oncreting,B rick m aso nry, S tone m aso nry, C uring, P lastering and F looring. Module four describesesse ntial w orking safety m easu res to avoid occu pational accidents. A nd finally, Module five

provides a list of literature w here useful inform ation regarding earthquake save house designingand construction principles are described.

Th e m erit of this m anual lies in the m od ular structured do cum en tation of inform ation from apractitioner for practitioners that allow s the design of various com bination of required practicaltraining.

A very tiny fraction of active m asons in G ujarat have received form al m aso nry training. Practicalconstruction skill and inform ation are transferred in an inform al w ay. B ecause of this system ,som e p ractices that are actually w ron g h ave n ow becom e goo d p ractice standard andtherefore som e p resent co nstruction q ualities are not up to professional quality standards inG ujarat.

There is a ge nu ine ne ed and high de m and for form al bu ilding construction training by m asons.S E W A has reco gn ised this as a h igh priority an d exp ressed the ne cessity o f profession al andpractical construction training m aterial for their construction related program m es. This BasicConstruction Training Manual for Trainers is the resu lting outcom e o f their expression.


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M O D U L E 1

M O D U L E 2

M O D U L E

3

M O D U L E 4

M

O D U L E 5

M O D U LE 1:

Basic Building Parts .................................................................. 7

M O D U LE 2:

Building Material and Quality Standards .......................... 19

M O D U LE 3:

Principles of Construction .................................................... 33

M O D U LE 4:

Safety .......................................................................................... 83

M O D U LE 5:

Earthquake resistant construction practices .................. 89


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Various parts of a building (Floor, wall, openings, roof, stair)

Basic Building Parts M O D U L E 1


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M O D U L E 1

Basic Building Parts

Content

1. Building......................................................................................................101.1. Foundation .................................................................................................101.2 Plinth .......................................................................................................... 111.3 Damp proof course (DPC).........................................................................121.4 Plinth beam................................................................................................121.5 Floor ...........................................................................................................131.6 Walls...........................................................................................................131.7 Openings....................................................................................................141.8 Stairs ..........................................................................................................151.9 Roof ............................................................................................................161.10 Surfaces / Finishes ....................................................................................16

2. Service facilities........................................................................................172.1 Water supply..............................................................................................172.2 Drainage and sewerage ............................................................................172.3 Garbage disposal ......................................................................................172.4 Electricity....................................................................................................17


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Basic Construction Training Manual for Trainers

1. BuildingA building provides shelter against natural elem ents such as rain, sunshine and w ind. It alsoprovides se cu rity and p rivacy. A building consists of the follow ing basic parts:

1.1. FoundationA foundation is n ecessary to evenly d istribute the entire building load on the so il in su cha m ann er that no dam aging settlem en ts take p lace. H en ce, the fou nd ation s ne ed to b econstructed on go od /solid grou nd

The Roof

The Lintel

The Window

The Door

The Cill

The Wall

The Floor

The DPC lies at theFloor Level right belowthe Walls (not under any

openings like Doors)

The Plinth lies betweenthe Floor and theGround

The Foundation isinvisible and lies belowthe Ground, just beneththe Walls

Water Supply

Drainage


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Steel reinforcement placingin foundation excavation

1.2 PlinthA plinth is norm ally co nstructed just above the ground leve l and im m ediately after thefoundation. It raises the floor above the ground level and herew ith preve nts su rface w aterfrom entering the b uilding.

Plinth construction height up to ground floor level

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1.3 Damp proof course (DPC)D am p p roo f course is a layer of w ater proofing m aterial such as asphalt or w aterproof cem ent.W alls are constructed above the dam p p roo f cou rse.

D am p proo f cou rse prevents su rface w ater from rising into the w alls.

D am pness reduces the s trength o f the w alls an d creates unhealthy living conditions. A lso itaffects the p aint and p laster and increasing the cost of m aintenance

D am p proo fing layer is not requ ired w he re a p linth be am is co nstructed , be cause the plinthbe am alread y pe rform s like a D PC .

Typical DPC type where no concrete plinth has been constructed

1.4 Plinth beamA plinth be am is constructed de pe nding up on the type of the structure of the building andnature o f the so il. It provides additional stability in regard to se ttlem ents o f the building an dearthquake d am ages.

Completed plinth beam of a building


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1.5 FloorThis is the surface on w hich w e do m ost of our activities. Floorings is laid over the filling of theplinth and o n subsequent floors.

Floo ring can be do ne w ith differen t m aterials, bu t care m ust be given that the groun d be lowthe floor is w ell com pacted. Flooring is don e to preven t dam pness from rising to the top andto have a firm platform that can be kept hyg ien ic an d clean.

Floor construction section, levelling sand, brick layer, cement cover and finishing work

1.6 WallsW alls are the vertical elem ents o n w hich the roof finally rests. Th ey can be m ade of differentm aterials like bricks, stones, m ud, co ncrete b locks, laterite blocks etc.

If the w alls are very long, colum ns can be provided to carry the roof.

W alls p rovide privacy and enclosure. W alls also provide security and protection against naturalelem en ts such as w ind , rain an d su nshine .

O pen ings are to be provided in w all for acce ss and ventilation.

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Ongoing brick wall (Rat Trap Bond) construction

1.7 OpeningsO pen ings are n orm ally provide d in the w alls as doo r, w indo w s and ve ntilators.

D oors provide access; w indow s and ventilators provide light and ventilation.

Building with many windows providing desired ventilation and light

Lintels are co nstructed just above the openings. It is norm ally a stone slab or a co ncrete slab .

S ill is the part of the w all that is just be low the w indow .Lintels are constructed to h old u p the w alls above the open ings.

In e arthquake prone areas a continuous lintel beam is provided all over the w alls.


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Continuous sill (direct bellow window)and lintel (direct above window)

1.8 StairsA stair is a seq ue nce of step s and it is provide d to afford the m eans of asce nt and de scentbe tw ee n the floo rs and land ing s.

Th e apartm ent or room of a b uilding in w hich stair is located is called staircase.

Th e space or ope ning occupied by the stair is called a stairw ay.

There are d ifferent kind of stairs are u se d in buildings, like R C C stair, w ooden stair, m etal stair,brick stair etc.

External stair construction, provides safe access to roof area

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1.9 Roof The roof provides p rotection for the building and the people living in it. The roof rests o n thew alls and req uires prop er ancho ring so that w ind and othe r m echanical im pact canno t de stroy

it. A roof can have different shap es b ut it is alw ays either flat or sloping.

R oof is typically m ade of R C C , stone slab , tiles e tc.

Clay tile covered roofs for rural housing scheme

1.10 Surfaces / FinishesE xternal finish es are the o uter m ost laye r of protection, w hich p rotect the s tructure fromw eathering .

Internal finish es are the laye rs g iven on internal faces. They g ive durab ility and pleasingappe arance to the inside.

Wall plastering and decorative structure design


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2. Service facilities2.1 Water supply

W ater supply facility is done to provide and distribute clean w ater inside the building.This can b e d on e throu gh a ne tw ork of pipe s. U sually pipe s used are o f P VC or G I pipe s.

2.2 Drainage and sewerageTh is is p rovided to collect and carry the w astew ater aw ay from the building.

2.3 Garbage disposalG arbage should b e collected and d isposed for creating hygienic living conditions.

2.4 ElectricityE lectrical connections are d one to provide p ow er supply for various needs inside the building.

M O D U L E 1



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Building material compilation at site (sand, grave, cement, concrete blocks)

M O D U L E 2

Building Material andQuality Standards


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Building Material and Quality Standards

M O D U L E 2

Content

Raw materials for masonry works ..........................................................22

1. Bricks..........................................................................................................221.1 Classification of bricks ..............................................................................22

1.1.1 Facing bricks..................................................................................2 31.1.2 Solid bricks ....................................................................................231.1.3 C avity bricks ..................................................................................2 31.1.4 Special shaped bricks ....................................................................23

1.2 Quality of bricks.........................................................................................231.2.1 A A class ........................................................................................2 41.2.2 Soaked bricks ................................................................................241.2.3 S tructure ........................................................................................2 41.2.4 Shape and size ..............................................................................24

1.2.5 Soundness.....................................................................................241.2.6 Fall test..........................................................................................241.2.7 Scratch test...................................................................................24

2. Stones .......................................................................................................252.1 Classification of stones .............................................................................252.2 Quality of building stone ..........................................................................26

2.2.1 S igns of good quality stones.........................................................262.2.2 Q uality tests ..................................................................................2 6

3. Concrete blocks.........................................................................................273.1 Classification of concrete blocks ..............................................................27

3.2 Quality of concrete blocks ........................................................................274. Sand and aggregates................................................................................28

4.1 Classification of sand and aggregates.....................................................284.1.1 C oarse aggregate ..........................................................................284.1.2 Sand ..............................................................................................2 8

4.2 Quality of sand and aggregates ...............................................................284.2.1 Sand storage .................................................................................294.2.2 Testing the sand quality ................................................................294.2.3 Sea sand ........................................................................................2 9

5. Cement ......................................................................................................305.1 Setting/Hardening......................................................................................305.2 Hydration of cement .................................................................................305.3 Different types of cement.........................................................................305.4 Type and quality........................................................................................30

5.4.1 C em ent storage .............................................................................305.4.2 U se of fresh cem ent.....................................................................31

5.5 Testing the cement quality .......................................................................31

6. Water..........................................................................................................326.1 Type and quality........................................................................................32

6.1.1 Seaw ater .......................................................................................326.1.2 C ollected rainw ater from roofs......................................................32

6.1.3 O ils ................................................................................................326.2 Water storage ............................................................................................326.3 Testing the water quality ..........................................................................32


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Raw materials for masonry worksTh e raw m aterials req uired for m asonry w ork, toge ther w ith the skill of the m ason are decisivefactors for the final quality of the m asonry w ork. Therefore, it is im portan t that the correct rawm aterials are used. B asic kn ow -how about the different required raw m aterials is essential form asons as w ell as supe rvisors.

The follow ing m ain raw m aterials for brick m asonry are ne ed ed :

n B ricksn Stonesn C on crete blocks

n Sandn C em ent mortarn W ater

1. BricksB ricks m ust be of good quality and w ithout visible cracks for a load-bearing w all. A hard ringingsoun d e m itted w hen tw o b ricks are struck together indicates that they h ave b een b urnt satis-factorily. G enerally, the bricks should be true to size and shape, w ith straight edges and evensurface, so as to facilitate laying them into position w ithout using too m uch m ortar. Inferiorbricks are g enerally unde r-bu rnt and as a co nsequence are e asily broken and are ve ry porous.Th ese are n eithe r hard n or durable and are incapable o f w ithstanding h eavy loads.

N ow all over the w orld, nearly all bricks are roughly the sam e shape and size that is ap prox:9 x 4 - 1/2 x 3 inches.

1.1 Classification of bricksTh ese are defined as suitab le for general building w ork having no special claim to give anattractive appearance. Th e type in use for m ost areas in India is classified as C om m on B ricks.

Pilling up of common bricks at production site, ready for selling

}


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1.1.1 Facing bricks

Th ese bricks are thoroughly burned and uniform in colour, and having plane rectangular facesand sharp straigh t righ t angled edg es. Th ey are used in the exp osed face of the brickw ork

w ithout any plaster or surface treatm ent. Th e bricks m ust have sufficient resistance tope ne tration by rain and w eathe ring agencies . In ge ne ral they are selected from a num be r ofbricks. Facing bricks are also used for R at Trap B ondm asonry w alls.

Facing bricks (second quality) stored at construction site

1.1.2 Solid bricks

A so lid brick is a b rick w ith less h oles or perforations of 25% of its vo lum e, in w hich frogs donot exceed 20% of its volum e.

1.1.3 Cavity bricks

A bu rnt clay ho llow block or brick w ith h oles large r than 20 m m w ide , w hich exce ed 20 % of itsvolum e.

1.1.4 Special shaped bricks

These are usu ally solid b ricks o f various sh ap es suited to a p articu lar construction.

1.2 Quality of bricksG en erally com m on bricks are g rou pe d into 3 classes:

Description Class 1 Class 2 Class 3

Water absorption M ax. 20% M ax 20% M ax 20%

Crushing strength M in. 105 kg/cm 2 M in. 70 kg/cm 2 M in. 35 kg/cm 2


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1.2.1 AA class

B ricks w ith crushing strength not less than 140 kg/cm 2 are grade d as A A class.

1.2.2 Soaked bricks

The stren gth of a brick decreases by about 25 % w he n soaked in w ater.

1.2.3 Structure

B rick w he n broken sho uld be ho m og en eous in structure, com pact and free from ho les, cracks,fissures, air bubbles, lum ps, pebbles and stones an d particles of lim e etc.

1.2.4 Shape and size

Th e brick shou ld be rectangular w ith straight and sharp e dges. A ll bricks should have the sam edim en sion s and no broken corners or edge s.

The size o f the bricks varies slightly from region to region in India. S tan dard size is norm ally23 0 x 115 x 70 m m (9 x 4-1/2 x 2-3/4 inch).

N o dim ension of a class 1 brick is allow ed to vary m ore than 3 m m from the stand ard size.

1.2.5 Soundness

The quality of a brick is good if there is a clear ringing sound w hen tw o b ricks are strucktogether.

1.2.6 Fall test

A brick shou ld no t break w he n d rop ped flat on hard grou nd from a he igh t of abo ut one m eter.

1.2.7 Scratch test

A good b urned brick has surface so hard that the fingernail cannot scratch it.


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2. StonesB uilding stones are derived from various types of rocks that are found in the crust of the earth.They are natural products an d are u sed directly, exce pt for their rough sizing and dressing,before being put in a structure.

S tones are or can be used in alm ost all parts o f construction such as foundations, w alls, floors,roofs, as w ell as for roads, dam s e tc.

A s a roug h guide, w alls w ith w ell fitting stones laid in cem ent m ortar have a strength of about75 % of an equ ivalen t brick w all, and w alls m ade of rou gh ston es h ave a stren gth of abou t 50 %of the equivalent brick w all.

C rush ed and broke n ston es are used in m aking concrete and artificial ston es such as concreteblocks.

All size bolder stone deposit Sized stone deposit

All size bolder stone try masonry wall Sized stone pillar construction

2.1 Classification of stonesS ton es or rocks are d ivided into three m ain g roups:

n Igneou s (G ranite)n S ed im en tary (S and-stone Lim e-ston es)n M etam orphic (S lates, M arble, Laterite)


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2.2 Quality of building stoneTh e fundam ental req uirem en ts of building ston es are stren gth, de nsity and durability com bine dw ith reasonable facility for w orking. A goo d bu ilding ston e m ust be hard, tou gh , com pact

grained and u niform in texture and color.

U sually, crystalline and close -grained stones are durab le.

2.2.1 Signs of good quality stones

Colour: S ton es should have un iform colour. R ed and brow n shades andm ottled colour indicate the prese nce of injurious m aterial.

Weight: B asically, the heavier and com pact grained ston es are the stronger anddu rable the y are.

Water absorption: A stone absorbing less w ater is stron ger and m ore du rable as it w ill

have less action of rainw ater.Appearance: A good building stone shou ld be free from decay, flaw s, veins, cracks

and sand-ho les

2.2.2 Quality tests

Th ere are several tests p ossible to define the quality o f a stone. H ow ever, in the field there arebasically three tests w here one can d efine the suitab le q uality of a stone.

Hammer testTake a ham m er and check the stone for its sound . A hard ring ing sound indicates that the ston e

is of go od q uality and h as no m ajor de fect such as h oles or cracks.

Visible testC heck the stone for any defects su ch as cracks, patches w ith soft m aterials, disco loring etc.

Porosity or absorption testW eight a stone o f reaso nable size an d p lace it for 24 h rs. into a w ater-bucket. A good b uildingston e sh ou ld not absorb m ore than 5% of its w eigh t of w ater after 24 hrs im m ersion .


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3. Concrete blocksC on crete b locks are now adays very com m on and tim e proo fed w alling m aterials. C on creteblocks can b e prod uced by hand and by m achine . H and m ade blocks are usually of low erqu ality, be cause m achine m ade blocks are be tter com pacted by a vibrator table. Th e specificuse of a co ncrete block de fine s its size an d the qu ality. C em en t and coarse sand w ith sm allsize aggreg ates are used w ith very low w ater/cem en t ratio.

H ollow blocks h ave better therm al properties than solid blocks of the sam e m aterial and totalthickn ess.

H ollow blocks have certain advantages over bricks, they are o nly about 1 3 rd of the w eigh tof the sam e n um be r of bricks and they can be laid abo ut fou r tim es rapidly and are o f am plestren gth for all purposes for w hich ordinary b ricks are used except under concentrated loads.They have the advantages of hollow w alls as reg ards insu lation against heat and soun d.

Concrete hollow block (CHB)production yard CHB wall construction used in earthquakeresistant house design

3.1 Classification of concrete blocksC oncrete b locks are classified into tw o m ain groups;

n S olid blocksn H ollow blocks

3.2 Quality of concrete blocksTh e basic quality requirem ent of concrete blocks are; strength, uniform in size and to a ce rtainde gree w ater resistant. A goo d co ncrete block is prod uced and stored und er a sun shade,has an appropriate m ix ratio (not m ore than 1: 6 for hollow blocks and 1: 10 for so lid blocks)contains clean raw m aterials (sand, aggregates and w ater) and fresh cem en t, is properly curedfor 21 days an d is hand led w ith care u p to the po int of use for m asonry w ork.

Description Solid blocks Hollow blocks(non load bearing w alls)Hollow blocks

(load bearing w alls)

Density > 1800 kg/cum > 1500 kg / cum > 1500 kg/cum

Crushing strength(after 28 days) M in. 5 N /m m

2 M in.2.8 N /m m s M in. 3.5 N /m m 2


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4. Sand and aggregatesSand and aggregates are very e ssential building construction raw m aterials and de serve specialattention.

4.1 Classification of sand and aggregatesM aterial retained on a 4 .75 m m IS (Indian S tandard) sieve is classified as coarse aggregate,and below that size as fine aggregate or san d. Th e m aterial passing a 75-m icron IS sieve isgenerally considered to be clay, fine silt or fine dust in an aggregate.

S and , w hich contains 9 0% of particles o f size greater than 0 .06 m m and less than 0.2 m m , isfine sand.

S and , w hich contains 9 0% of particles o f size g reater than 0.6 m m and less than 2 m m iscoarse sand .

4.1.1 Coarse aggregate

There are m ainly three sou rces from w he re co arse agg reg ates o riginate nam ely:

n N atural depositsn C rushe d stonesn B rick aggreg ates

4.1.2 Sand

There are m ainly fou r types o f sand nam ely:

n P it sandn Se a sandn R iver sandn C rushed sand

Pit sand deposit


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4.2 Quality of sand and aggregatesThe quality o f the m ortar is d irectly linked to the characteristics and condition of the sand. S andand aggreg ates m ust be free from clay, loam , veg etables and any othe r organic m aterial.

C lay or dirt coating on agg reg ates prevents adhe sion of cem en t to ag greg ate, slow s dow n thesetting and harde ning process an d red uce s the stren gth of the m ortar.

Th erefore, clay and silt conten t shou ld n ot exce ed 10% , othe rw ise the sand n ee ds to b ew ashed.

4.2.1 Sand storage

Th e sand should be stored preferably und er a sh ade. Th e sand should be sufficien tly protected ,su ch that no im purity from an im als, ag ricu ltural w aste, children, trees, etc. is p ossible.

4.2.2 Testing the sand quality

There are tw o m ain san d quality-testing m etho ds, nam ely:

Visible testC he ck the sand for im purities such as organic m aterials (m ud , leaves, roots etc.) R em ove thembe fore u sing the sand.

Clay and silt content testThe clay an d silt conten t test can be in tw o w ays:

Hand testThe san d sam ple is rub be d b etw ee n d am p h and . A clean sand w ill leave the han ds o nly sligh tlystained. If the hands stay dirty, it indicates the presence of too m uch silt or clay.

Bottle testTake a bottle and fill in the sand until it is half full. Fill in clean w ater un til the bottle is three-quarters full. S hake up vigorously and leave it to se ttle for about one hour. C lean sand w illse ttle im m ediately, silt an d clay w ill se ttle slow ly on top of the sand. The thickn ess of the clayand silt layer shou ld n ot exceed o ne -ten th o r 10% of the sand be low .

This test is also called decantation test. This test is not applicable to crush ed stone sands!!

D irty sand shou ld never be used in m asonry because it w ill red uce the adh esive value of them ortar considerably.

4.2.3 Sea sand

S ea san d is u nsu itab le for m ortar as it co ntains salts, w hich attract an d retain m oisture. Inaddition the salt content in the m ortar w ill produce a w hitish pow der of effloresce nce, w hichdisco lors the brickw ork or m asonry.


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5. CementC em ent is a m ixture o f 60 to 6 7% lim e, 17 to 2 5% silica and 3 to 8 % alum ina, w hich areintim ately m ixed together w ith w ater to form into a slurry, w hich is su bsequently heated, dried,calcine d and groun d to a ve ry fine pow de r. A sm all prop ortion o f gypsum is adde d b eforegrinding in order to co ntrol the rate of setting.

5.1 Setting/ HardeningThe term s setting an d harde ning have d ifferent m eanings. Setting is the process w hich chang esa fluid concrete to a so lid but w eak state. H arde ning is the process by w hich the w eak se tconcrete attains strength.

5.2 Hydration of cementW he n w ater is added to cem en t, the cem en t hydrates and during the chem ical reaction s, w hichtake place w hile the cem ent is se tting , an increase in tem perature occurs an d a considerablequantity o f heat is g enerated

5.3 Different types of cementTh ere are total five different kinds o f cem ents. C em ents are classified by their properties andchem ical com position . The nam es of these five kind s o f cem en ts are:

n O rdinary Po rtland C em entn R apid hardening Ce m entn Q uick setting C em entn B last furnace S lag C em en tn H igh A lum ina C em ent

5.4 Type and qualityFor ordinary brick m asonry w ork it is recom m en de d to use ordinary Po rtland cem en t. In orde rto ach ieve a good m ortar in strength an d durab ility, it is essential that the follow ing rules andregulations be follow ed:

5.4.1 Cement storage

C em en t can be safely stored in bag s for a few m on ths if kep t in a dry roo m . Pape r bag s arebetter for storing than jute bags b ecause paper bags p erform be tter in regard to qu ality d ete-rioration du e to m oisture. D uring the m onsoo n tim e, the cem en t storage plays an even m oreim portan t role, since the relatively higher hum idity acce lerates the deterioration proce ss o f thecem ent.

C em en t bags shou ld b e stored on a raised w oo de n p latform (e.g. tim be r pallets) abou t 15 to20 cm above the floo r level and abo ut 30 to 5 0 cm aw ay from w alls.

The cem en t stack should n ot be m ore than 10 bags h igh . The bags sho uld be placed closetogether to reduce circu lation of air.

A cem ent bag sho uld never be op ened un til its im m ediate u se for m ixing .


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5.4.2 Use of fresh cement

O rdinary Portland ce m en t, w hich has bee n stored for over six m on ths, shou ld n ot be used form asonry w ork.

Th e average reduction of strength in a 1:2:4 m ix as a result of storage is:

Fresh cement strength 100%C em en t after 3 m on ths, stren gth reduce d by 20%

C em en t after 6 m on ths, stren gth reduce d by 30%

C em ent after 12 m onths, strength redu ced by 40%

C em en t after 24 m onths; stren gth reduce d by 50%

5.5 Testing the cement qualityThe ind ication of dam age d cem en t is given by the prese nce of large lum ps of set cem en t.These lum ps o f set cem ent should n ot be used, no t even if screene d ag ain.

The freshn ess of cem en t can be tested as per follow ing de scription :

Lump test:C heck the cem ent for any sm all or large lum ps. R em ove them .

Rubbing test:W hen cem ent is rubbed betw een finge rs and thum b it shou ld fee l like a sm ooth p ow der such

as flour.

Setting test:If you are u ncertain about your cem ent quality you can m ake a sim ple setting test.

M ake a stiff paste o f ne at cem en t and w ater and form it into a cake abou t 75 m m diam eterand 12 to 15 m m thick. The cake shou ld co m m ence to set in ab out 30 to 60 m inutes. In 18 to24 hours the cake should have hardened sufficiently so that it does not effortlessly scratch thesurface w ith a thum bnail.


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6. WaterTh e w orkability o f a m ortar increases as the w ater con ten t of the m ix is increased. W aterlubricates the m ixture. H ow ever, increase d w ater content w ill cau se a decrease in s trength,produce cracks (shrinkage) and d ecrease den sity.

Th erefore, not only the quality, but equally im portant the quantity of the w ater is im portan t forprod ucing a good m ortar and brick m asonry w ork.

6.1 Type and qualityA lm ost any natural w ater that is drinkable and has no p ron ou nced taste or od or can be use d asm ixing w ater for m aking cem en t m ortar. W ater suitable for m aking cem en t m ortar, how ever,m ay not be fit for drinking.

6.1.1 SeawaterS eaw ater should not be used as m ixing w ater for cem en t m ortar.

6.1.2 Collected rainwater from roofs

R ainw ater collected from roo fs can be used for m ixing m ortar or concrete.

6.1.3 Oils

Various kinds of oil are occasionally p resent in m ixing w ater. W ater m ixed w ith any kind of oilshall no t be u sed for m ixing m ortar or concrete.

6.2 Water storageW ater shou ld be stored w he re no con tam ination is p ossible. W ater stored in clean drum sor covered tanks is p referred. Th e age of the w ater, or the storage tim e does not affect thecem en t m ortar qu ality in any w ay.

6.3 Testing the water qualityW ater of qu estion able suitability can be used for m aking cem en t m ortar cube s. Th e w ater inqu estion shou ld ach ieve the streng th in 7 and 2 8 d ays eq ual to at least 90 % of com parablespecim ens m ade w ith drinkable w ater.


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Bad brick wall construction resulting into corner collapse / damage

Principles of Construction

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Content

1. Principles of mortar .................................................................................381.1 What is mortar?.........................................................................................381.2 Type of mortars .........................................................................................381.3 Cement mortar...........................................................................................381.4 Lime mortar ...............................................................................................381.5 Cement lime mortar ...............................................................................381.6 Mortar sand granulation ...........................................................................381.7 Mixing mortars ..........................................................................................39

1.7.1 W eight m ethod..............................................................................391.7.2 Volum etric m ethod ........................................................................39

1.8 Categorization of mortars and its mix ratio ............................................391.9 Dos and donts ..........................................................................................40

2. Principles of concreting............................................................................422.1 What is concrete?......................................................................................42

2.1.1 O ther ingredients ..........................................................................422.1.2 H ydration begins ...........................................................................422.1.3 The form s of concrete ...................................................................43

2.2 Functions and requirements of concrete ingredients.............................432.2.1 Functions of cem ent......................................................................432.2.2 Functions of sand ..........................................................................432.2.3 C oarse aggregate ..........................................................................442.2.4 W ater.............................................................................................44

2.3 Reinforced concrete .................................................................................44

2.4 Reinforcement ..........................................................................................442.4.1 Type and characteristics of steel bars ..........................................442.4.2 C ategories & purpose of reinforce m ent........................................452.4.3 B asic rules for steel reinforcem ent...............................................45

2.5 Type of concrete .......................................................................................462.5.1 H igh strength concrete..................................................................462.5.2 M edium strength concrete ............................................................462.5.3 Low strength concrete ..................................................................462.5.4 M ixing proportion of concrete .......................................................46

2.6 Cover in concrete ......................................................................................472.7 Requirements of concrete.........................................................................47

2.7.1 S trength .........................................................................................472.7.2 W orkability .....................................................................................4 7

2.8 Factors influencing concrete quality........................................................472.8.1 C em ent..........................................................................................4 72.8.2 W ater C em ent ratio ....................................................................472.8.3 R aw m aterials................................................................................472.8.4 Fineness of fine aggregate ............................................................482.8.5 P lacing the concrete ......................................................................482.8.6 C om paction ...................................................................................492.8.7 C uring ............................................................................................492.8.8 E ffect of aging ...............................................................................49

2.9 Mixing of concrete ....................................................................................492.9.1 H and m ixing ..................................................................................49

2.9.2 M achine m ixing ............................................................................502.10 Dos and donts ..........................................................................................502.11 Form work..................................................................................................532.12 Removal of the forms ...............................................................................54


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3. Principles of brick masonry......................................................................553.1 Brick overlap between layers ...................................................................553.2 Size of bricks..............................................................................................55

3.2.1 N am es of parts of a brick ..............................................................563.3 Rules for joints ..........................................................................................573.3.1 H orizontal joints .............................................................................573.3.2 Vertical joints .................................................................................57

3.4 Selection of bricks .....................................................................................583.5 Brick cuttings .............................................................................................583.6 Brick soaking..............................................................................................583.7 Maximum brick wall height per day ........................................................593.8 Curing.........................................................................................................593.9 Pointing ......................................................................................................593.10 Most common bonds ................................................................................60

3.10.1 Flem ish bond (O ne brick thick)......................................................603.10.2 Flem ish bond (O ne and half brick thick)........................................603.10.3 English bond (O ne brick thick).......................................................613.10.4 English b ond (O ne and h alf brick thick ..........................................613.10.5 R at trap bond.................................................................................623.10.6 S tretcher bond ...............................................................................633.10.7 H eader bond ..................................................................................64

4. Principles of stone masonry ....................................................................654.1 Stone surfaces ...........................................................................................654.2 Rules for stone shaping ............................................................................65

4.2.1 Line stones....................................................................................664.2.2 C ornerstones .................................................................................664.2.3 A rch stones ..................................................................................67

4.3 Unsquared rubble masonry ....................................................................674.3.1 U ncoursed rubble ..........................................................................674.3.2 R andom coursed rubble ................................................................684.3.3 C oursed rubble ..............................................................................68

4.4 How to build with shaped stones ............................................................684.5 Bonding......................................................................................................704.6 Curing.........................................................................................................704.7 Pointing ......................................................................................................704.8 Dos and donts ..........................................................................................71

5. Principles of curing...................................................................................725.1 What is curing?..........................................................................................725.2 Type of curing ............................................................................................72

5.2.1 W ater curing ..................................................................................725.2.2 Vapor curing ..................................................................................735.2.3 S team curing .................................................................................73


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6. Principles of plastering.............................................................................746.1 What is plastering? ...................................................................................746.2 Requirements of good plaster ................................................................74

6.3 Types of mortars for plastering................................................................746.3.1 C em ent m ortar..............................................................................746.4 Number of coats of plaster.......................................................................74

6.4.1 B ackground ....................................................................................756.4.2 Tw o coat plaster............................................................................756.4.3 Three coat plaster .........................................................................756.4.4 S ingle coat plaster ........................................................................75

6.5 Preparation of background ......................................................................756.6 Recommended mortar mixes ...................................................................766.7 Defects in plastering .................................................................................77

6.7.1 B listering of plastered surface.......................................................776.7.2 C racking .........................................................................................77

6.7.3 C razing...........................................................................................7 76.7.4 E fflorescence ...............................................................................776.7.5 Flaking ...........................................................................................7 76.7.6 Peeling ...........................................................................................7 76.7.7 Popping..........................................................................................776.7.8 R ust stains ....................................................................................786.7.9 U neven surface .............................................................................78

7. Flooring......................................................................................................797.1 What is flooring? .......................................................................................797.2 Components of flooring ..........................................................................79

7.2.1 Sub floor........................................................................................7 9

7.2.2 Floor finish.....................................................................................7 97.3 Types of floors ...........................................................................................797.3.1 B rick bat floor ...............................................................................7 97.3.2 C oncrete floor................................................................................807.3.3 O ther com m on types of floors......................................................81


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1. Principles of mortar1.1 What is mortar?

M ortar m ay be defined as a m aterial com posed of fine aggregate and cem en t, w hich form s ahardene d m ass after m ixing w ith w ater. It is used in the b eds and side joints of m aso nry w ork,in order to bind the stones, bricks o r blocks together and distribute the pressu re throughoutthe block-w ork.

M ortar is further used also for plastering w ork, pointing w ork, flooring and topping w ork.

G oo d m ortar used for m asonry consists of cem en t, sand an d w ater in the correct prop ortion s.W he n the m aterials are freshly m ixed , m ortars have a p lastic co nsisten cy, w hich cou ld beeasily w orked w ith trow els to fill the joints in m asonry or to render the surfaces of w alls byplastering etc. B y the virtue of the se tting properties o f the binding m aterial used (ce m ent,lim e) they set and be com e hard subseq uently.

1.2 Type of mortarsG en erally the re are three co m m on types o f m ortars in u se for m asonry and plastering w ork,nam ely:

n C em ent m ortarn Lim e m ortarn C em ent lim e m ortar

1.3 Cement mortar

C em ent m ortar is now adays the m ost com m on ly used m ortar for brick as w ell as ston esor concrete block m aso nry w ork. It provides h igh strength properties. M ix proportion variesaccording to req uirem en ts o f the m asonry structure.

1.4 Lime mortarTh is is a m ixture of quicklim e (burnt lim estone) and sand in the proportion of 1 part lim e and 3parts sand, in addition to w ater. Lim e m ortar w as o nce the principal m aterial used for beddingand jointing bricks and stones. It is u sed less frequently now as it deve lops strength veryslow ly and is not easily availab le in the m arket.

1.5 Cement lime mortarThis w as the m ost usu al ge neral-purpo se m ortar com prising 1 part cem ent 2 parts lim e and 9parts san d. Th e addition of lim e im prove s the w orkab ility and m akes it easier to use. C em entlim e m ortar is m ainly used for internal w ork.

1.6 Mortar sand granulationThe sand use d for every kind of m ortar m ust be clean and free from clay and othe r organ icm atters.

For getting a proper m ortar, the g ranulation o f the sand n eeds to b e correct. S and w ithout fines

(be low 0.5m m ) gives a harsh m ortar w ith a low com pressive stren gth an d a bad w orkability.C em en t m ortar gives the best resu lt w he n the sand com prises of the follow ing :


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0 - 0.5 m m (60% 0-0.2 m m ) 1 part0.5 - 2 m m 1 p art2 - 4 m m 1 p art

1.7 Mixing mortarsTh e sand is placed o n a clean p latform , the correct am ou nt of cem ent is adde d to it, both, sandand cem ent are thoroughly m ixed before w ater is add ed and the m ass gradually w orked up intoa p lastic condition. Th e gene ral rule is that sand and cem ent are m ixed dry together at least 3tim es before w ater is added. This is im portan t for achieving the proper plasticity.

Flatten the dry mix with a trowel, if properlymixed a uniform gray color is visible.

Add water only once a uniform gray color isvisible.

1.7.1 Weight methodM ortar m ixtures are also expressed in kg of cem en t pe r 1 m 3 of cem en t m ortar. For exam pleP C 25 0 m ean s that 25 0 kg o f Po rtland C em en t (P C ), approx. 1000 liters of sand and 120 litersof w ater are use d to o btain abo ut 1 m 3 m ortar. Th is m etho d is m ainly used for large construc-tions in cities for bridges, hotel and shopping com plexes etc.

1.7.2 Volumetric method

U sually on sm all and rural construction sites the m ore practical volum e b atching m ethod isapplied. Th e vo lum etric m ethod is a very appropriate w ay to m ix raw m aterials. S pecial carem ust be given to e nsure that the w orkers m easure each tim e the sam e volum e.

1.8 Categorization of mortars and its mix ratioM ortars are categorized in m ainly three group s, nam ely:

Group 1H ighly stresse d m aso nry incorporating height strength structural units as used in m ultistoryload bearing b uildings.

G roup 1 batching

Cement Sand1 4

Bucket Buckets


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Group 2N orm al load bearing applications su ch as e xternal house w alls, parapets, and balustrades,retaining structures, freestanding garden w alls and o ther w alls expo sed to se vere dam pne ss.

G rou p 2 batching

Cement Sand

1 6

Bucket Buckets

Group 3Lightly stressed non-structural w alls

G rou p 3 batching

Cement Sand

1 8

Bucket Buckets

1.9 Dos and donts

Dos:U se alw ays-clean sand for m ortar.

Why?C ontam inated san d (e.g. roo ts, leaves, plastic parts, saw dust, anim al and hum an excreta etcw ill no t bind w ith cem en t, he nce is w eakening the m ortar. A lso sand w ith high pe rcen tage ofclay o r silt w ill w eake n the m ortar, because the clay or silt contains too m any fines that needsto be covered by cem en t for proper bind ing , he nce , the m ortar becom es w eak.

Sand deposit properly covered and protected from being contaminated


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Dos:A lw ays use fresh an d lum p free ce m en t for m ortar

Why?O ld cem en t is loo sing its stren gth prop erty. E .g. cem en t that has b ee n stored for abo ut 6m onths is gaining 30 % less strength than fresh cem en t. For good m ason ry w ork, stren gth isim portan t as it influence s the overall building quality.

Improperly stored cement results inloss of quality

Dos:A lw ays m ix the dry ing red ien ts (sand & cem en t) tog ethe r be fore ad ding w ater.

Why?W et sand particles have the ten de ncy to stick toge ther and are the refore hinde ring that cem entcan cover them . Th is results in an un-uniform m ix that is reducing the m ortar quality, becauseeach san d particle should ide ally b e fully cove red w ith cem ent.

Furthe r, add ing w ater tog ethe r w ith san d an d ce m en t in o ne go m akes m ixing the m ortarextrem ely d ifficu lt for the lab orers.

Dos:

A lw ays protect the m ortar-m ixing place from w ind , rain and sunsh ine .

Why?W ind and sun shine is entraining the w ater from the m ortar and is accelerating the harde ningprocess b efore it is being used. Th is is m akes the m ortar useless for any purpose . R ain isadding w ater and the m ortar becom es unusable too .

Donts:D o not use or re-use m ortar that has already harde ne d. A s ce m ent m ortar sets relatively quickly(approx. 30 m inutes), it should n ever be m ixed in h uge q uantities.

Why?In h ardened m ortar, the h ydration p rocess o f the cem ent has started and re-m ixing it isde stroying the bo nd be tw ee n ce m en t and sand . This bo nd cann ot reg ain stren gth ag ain bysim ply adding fresh w ater to the m ortar.


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harde ning , and stren gth develop m en t. O nce the con crete is tho rou gh ly m ixed and w orkableit should be placed in form s b efore the m ixture be com es too stiff. D uring placem en t, theconcrete is conso lidated to com pact it w ithin the form s an d to elim inate p otential flaw s, suchas h oneyco m bs an d air pockets. For slabs, concrete is left to stand u ntil the surface m oisturefilm disap pears. A fter the film disappears from the surface , a w ood or m etal handfloat is usedto sm ooth off the co ncrete. Floating produces a relatively even, but slightly rough, texturethat has good slip resistance an d is frequently u se d as a final finish for exterior slab s. If asm ooth, hard, dense surface is required, floating is follow ed by steel trow eling. C uring beginsafter the exposed surface s of the concrete h ave hardened sufficiently to resist m arring. C uringen sures the con tinu ed hydration of the cem en t and the stren gth gain of the con crete. C on cretesurfaces are cured by sp rinkling w ith w ater fog, or by using m oisture-retaining fabrics suchas burlap or cotton m ats. O the r curing m etho ds preve nt evapo ration of the w ater by sealingthe surface w ith p lastic or special sprays (curing com pounds). S pecial techniques are used forcuring concrete during e xtrem ely co ld or hot w eather to protect the concrete. Th e longer theconcrete is ke pt m oist, the stron ge r and m ore durable it w ill be com e. Th e rate of harde ning

de pe nd s upo n the com po sition and fine ne ss of the cem en t, the m ix prop ortion s, and them oisture and tem perature conditions. M ost of the hydration and stren gth gain take place w ithinthe first m onth of co ncretes life cycle, but hydration co ntinues at a slow er rate for m any ye ars.C oncrete continues to get stronger as it gets older.

2.1.3 The forms of concrete

C oncrete is p rodu ced in four basic form s, each w ith unique applications and prope rties. Readymixed concrete . Its batched at local plan ts for de live ry in the fam iliar trucks w ith revo lvingdrum s. Precast concrete products are cast in a factory setting. Th ese products b enefit fromtight quality co ntrol ach ievable at a p roduction plan t. Precast products rang e from con crete

bricks and paving stones to b ridge girders, structural com ponents, and panels for cladding.Concrete masonry , ano the r type of m anu factured con crete, m ay be be st know n for its con-vention al 8 8 16 - inch block. Todays m asonry units can be m olded into a w ealth of shapes,configurations, co lors, and textures to serve an infinite spectrum of building applications and ar-chitectural needs. C em ent-base d m aterials represent products that defy the label of concrete,yet share m any o f its q ualities. C onventional m aterials in this category include m ortar, grout,and terrazzo. S oil-cem ent and roller-co m pacted co ncrete-co usins of concrete-are use d forpavem ents and d am s. O the r products in this category includ e flow able fill and cem ent-treatedbases. A ne w ge ne ration of advanced prod ucts incorporates fibers an d special aggreg ate tocreate roofing tiles, shake sh ingles, lap siding, and countertops. A nd an em erging m arket is theuse of cem ent to treat and stabilize w aste.

2.2 Functions and requirements of concrete ingredients2.2.1 Functions of cementn It fills up the voids in the fine and coarse aggregates.n M ake the concrete im perm eable.n It provides streng th to concrete on setting and h ardening .n It binds the aggregates into a solid m ass by virtue o f its se tting.n H ardens w hen m ixed w ith w ater.

2.2.2 Functions of sandn S and fills the voids existing in the coarse aggregates.n It reduces shrinkage o f concreten S and h elps in h arde ning of cem en t by allow ing the w ater throu gh its voids.


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2.2.3 Coarse aggregaten It m akes solid and h ard m ass of concrete w ith cem en t and san d.n It reduces the co st of concrete, since it occupies m ore volum e.

2.2.4 Watern W ater w ets the surface of aggreg atesn It facilities the sp reading of cem ent ove r the ag gregates and m akes the m ix w orkable.n It initiates the hydration process o f the cem ent, subsequently starts the setting and

harde ning p roce ssn It con trols the he at ge ne rated by the hydration process of the cem en t

2.3 Reinforced concrete

C oncrete can support heavy loads in com pression, but its tensile strength is relatively low .(A bo ut one tenth of the com pressive) To com pen sate for the low tensile strength property o fthe concrete, stee l bars w ith a ve ry h igh tensile streng th is com bined w ith concrete.

B y em be dd ing stee l bars in the concrete, advantage is taken of the se prop erties to im provethe load carrying capacity of the structure. The steel is place d in the concrete that is subjectedto tension but also to avoid cracks due to shrinking.

2.4 Reinforcement2.4.1 Type and characteristics of steel bars

S teel is a high stren gth m aterial and for reinforced concrete w ork m ild steel, m edium tensilesteel, high tensile steel and h ard d raw n steel is com m only used.

D ifferent size o f reinforcem ent & their w eights:

Sr.No. Size of Steel (dia in mm) Weight per Rm.

1.2.3.

4.5.6.7.

68

10

12162025

0.22 kg0.39 kg0.62 kg

0.89 kg1.58 kg2.47 kg3.85 kg


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Th e variou s form s in w hich stee l is used as reinforcem en t in R .C .C . w orks are rou nd bars,de form ed bars, tw isted bars, square bars and flats. S om e tim es expand ed m etal fabrics m adeby w elding steel w ire in the form square m esh, are also used as reinforcem ent in slabs.

M ild stee l and m ed ium ten sile stee l bars of rou nd section s are m ost com m on ly use d in R .C .C .w ork. Th e diam eters of round bars used in no rm al building w ork are 6, 8,10, 12, 16,18 , 20, 22,2 5 an d 32 m m .

D eform ed bars or high yield streng th d eform ed b ars are furnished w ith lug s, ribs or other formof surface deform ations for the purpose of increasing their bon d strength w ith concrete.

2.4.2 Categories & purpose of reinforcement

There are tw o m ain categ ories and pu rpo ses of reinforcem en t by stee l.

The main reinforcement, to take care for the tension force s.

Distribution reinforcement, to spread the load and to keep the m ain reinforcem en t inposition during casting.

2.4.3 Basic rules for steel reinforcement

Th e m ain reinforcem en t shou ld alw ays be at the place w he re ten sion occurs. It shou ldadequately cove red by concrete to avoid corrosion of the reinforcem ent. S teel bars o f plainsurface (m ild steel) need to be h ooked at the e nds to o btain b etter adhesion, and thereforecreate a g reater strength for the structure. H ooking is not necessary for steel bars w ith ribbedsurface (Tor-steel).

A prop er bo nd be tw ee n the stee l rod s and the concrete is the m ost im po rtant for reinforcedconcrete. Th e surface of the rod has to be clean. In orde r to provide a p rop er bond the rod shave to be surrou nd ed com pletely b y the concrete. Th erefore, the reinforced concrete has tobe prop erly vibrated . P lain bars m ust have en ds w ith ho oks, w hich, shou ld be anchored , inthe pressure zone . D eform ed bars w ith ribb ed projection s can have straigh t en ds bu t the n theanchorage h as to b e in the p ressure zone o f the structure.

If rod s have to be overlappe d the follow ing rules show the m inim um overlap len gth:

R od w ith hook - 45 tim es diam eter of the rod

S traight - 65 tim es diam eter of the rod

Important:Th e proper placing of reinforcem ent for structures of high q uality co ncrete requires a w orkingdraw ing or reinforcem ent plan , containing all the necessary inform ation. A structural engineerw ill m ake this reinforcem ent plan only.


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2.5 Type of concreteThe stren gth o f the con crete d ep en ds on m ix prop ortion s and sh ou ld su it the w ork being do ne .D ifferent applications require different strengths of concrete. Three different strength categoriesw ith typ ical ap plications are outlined below

2.5.1 High strength concrete (M 300 M350)

H igh stren gth co ncrete sh ou ld b e u sed for suspen ded structural beam s and slabs, precastitem s (stairs) an d heavy-duty floors.

2.5.2 Medium strength concrete (M 200 M250)

M edium strength concrete is su itable for reinforced foundations an d slabs, light duty housefloors, paths, steps, drivew ays and garage doors.

2.5.3 Low strength concrete (M100 M150)

Lo w strength concrete is su itab le for unreinforced foundations for houses an d freestandingw alls.

2.5.4 Mixing proportion of concrete

Concrete Type Proportion of Cement Proportion of Sand Proportion of Aggregates

M 100M 150M 250M 350

1111

4432

6432


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2.6. Cover in concreteA n appropriate concrete cover of the steel reinforcem ent is ab so lutely esse ntial to protect thestee l m em be rs from w eathe ring effects. A s soon as air contacts the stee l m em be rs inside the

concrete, the oxidation proce ss starts, lead ing to rusting and eventually disintegration of theaffected part. Th is can lead to serious consequences such as the collapse of a beam or slab.

M inim um requirem ent of cover in concrete m em bers:

Members Minimum reinforcement cover

S lab 15 0 m m

Beam 25 m m

C olum n, Fou ndation 40 m m

2.7 Requirements of concrete2.7.1 Strength

The co ncrete m ust be stron g e no ug h to b ear the im po sed stresse s safely in e ach w ith therequired factor of safety. It w ill be uneconom ical m aking the concrete stronger than desired,bu t at the sam e tim e its m inim um strength m ust be ensured .

2.7.2 Workability

The con crete m ix use d sh ou ld b e su ch that it can be easily m ixed , placed , com pacted andfinished at surface w ith m inim um of effort i.e. the concrete should be w orkab le.

2.8 Factors influencing concrete quality2.8.1 Cement

Th e cem ent quality is a ve ry im port factor that influences the basic requirem ent of theconcrete. C em en t m ust be fresh and free from any lum ps. The grading of the cem en t isim po rtant too . A high grade cem en t, e.g. G rade 53 is gaining m ore rapid stren gth than a G rade33 cem en t. H ow ever, after 90 days, bo th type of cem en t w ill have app rox. gaine d the sam efinal strength.

2.8.2 Water Cement ratioTh e ratio o f m inim um quantity of w ater to the w eigh t of cem ent, req uired to obtain the desiredconsistency and w orkab ility o f concrete m ix is called: w ater cem ent ratio. C oncrete strengthde creases w ith the increases in w ater cem ent ratio. Th is is be cause the adde d w ater on ceevap orated leaves be hind very very sm all voids. Th e m ore vo ids the re are in a co ncrete, thew eaker it becom es.

2.8.3 Raw materials

The sand and ag greg ate m ust be free of leaves, grass and o the r foreign m atters. S and sh ou ldbe fairly co arse w ith particle sizes ranging from fine dust up to about 5m m .

C lean agg regate w ith sizes of 26,5 m m , 19 m m , 13,2 m m or 9,2 m m can be used for concrete.A gg reg ate size of 26 .5 m m can b e used for thick section such as fou nd ation s, de ep susp en de d


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slabs and ind ustrial floors thicker than 120 m m . 19 m m aggregates can be used for floo rs, pathsand drivew ays. A ggreg ates 13 ,2 m m or 9,5 m m can be used for thin concrete section such asthin suspe nded slabs, precast item s w ith se ction thickness rang ing from 40 m m to 5 0 m m .

2.8.4 Fineness of fine aggregate

C oncrete strength decreases w ith increases in fineness of fine aggregate. Th is is because thefines require a lot of ce m ent for a total coverage, resu lting into a leaner overall m ix.

2.8.5 Placing the concrete

C oncrete after m ixing m ust be placed in the defined position and com pacted before the initialse tting o f cem ent starts.

B efore placing of concrete starts, it m ust be ensured that the form s are rigidly brace d, true to

their position, oiled, clean ed an d dried of any stan ding w ater.S pecial care m ust be take n that before placing the concrete that the steel reinforcem ent isprop erly distanced from the form w ork to e nsu re ap prop riate coverage of the stee l m em be rs.

P lace the concrete as close to its final position as possible. I f concrete is p laced on thegrou nd , the soil sho uld be tho rou gh ly dam p, bu t w itho ut any stand ing w ater w he n the con creteis p laced. W ork the concrete righ t into the corne rs an d alon g the edg es on the form or holew ith a spade or a trow el.

Concrete should never be dropped from a height, as it will cause segregation.

wrong: placing heaps causes segregation


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2.8.6 Compaction

It is extrem ely im portant that the concrete is thoroughly co m pacted im m ediately after placing into the form s. N ot properly co m pacted concrete results into so called honey com bspots that

expose the steel reinforcem ent to air and resu lting in rusting. B esides, not properly com pactedconcrete has a red uced be aring capacity an d is overall w eakening the casted structure. Avibrator need le can achieve be st com paction.

2.8.7 Curing

A fter con crete is p laced, a satisfactory m oisture conten t and tem perature (be tw ee n 50 Fand 75F) m ust be m aintained, a p rocess called curing. A dequate curing is vital to quality

concrete. C uring has a strong influe nce on the prope rties of harden ed concrete such asdurab ility, strength, w atertightness, ab rasion resistance , vo lum e stab ility, an d resistance tofreezing and thaw ing and deicer salts. E xposed slab surface s are especially sensitive to curing.S urface strength d eve lopm ent can be reduced significan tly w hen curing is defective. C uringthe concrete aids the che m ical reaction called hyd ration. M ost freshly m ixed concrete containsconside rably m ore w ater than is req uired for com plete hydration of the cem en t; how ever, anyappreciab le loss o f w ater by evap oration o r otherw ise w ill delay or prevent hydration. If tem -peratures are favorab le, hydration is relative ly rapid the first few days after co ncrete is placed;retaining w ater during this period is im portan t. G ood curing m eans evaporation should b eprevented or red uce d

2.8.8 Effect of aging

B asically if all rules and regulation for concreting are p roperly follow ed, concrete g ains strengthby aging. H ow eve r, the rate of increase in strength decreases w ith tim e.

2.9 Mixing of concreteM ixing o f concrete is usually m ade by hand for sm all quantities or by m achine for bigquan tities.

2.9.1 Hand mixing

H and m ixing is ad op ted w he re in sm aller quantities of aggregates is involved or the involvem entor procuring of m ixing m achine s is o ut of reach. M ixing shall alw ays b e do ne on w atertigh tplatform in o rde r to avoid ce m en t w ater see page .


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Procedure for proper hand mixing:n S pread the m easured qu antity of sand in a layer of abo ut 10 cm on the m ixing platform .n P lace the cem en t on top of the sand and m ix the tw o tho rou gh ly tog ethe r un til thy form

an eve n color.n P ile the m ixture into a heap an d m ake a hollow in the m idd le.n Pour in w ater slow ly in sm all quantities and m ix until a sm ooth p aste is form ed.n A dd now the correct am ou nt of aggreg ate an d m ix un til every agg reg ate is prop erly

coated.

2.9.2 Machine mixing

M achine m ixing is required for large quantities o f concrete w ork and for good w orkab ility forplacing the concrete in a sh ort tim e and w ith no w astage.

C on crete having coarse agg reg ates is m ixed in con crete m ixers.

Procedure for machine mixing:n M easure the quantities of each ingredien tn First add the agg reg ates and som e am ount of w ater, the n the cem en t, then the sandn M ix and ad d m ore w ater until the right consistency is reache dn E m pty the m ixer com pletely w he n discharging e ach batch.n C lean the con crete m ixer tho rou gh ly on com pletion .

2.10 Dos and donts

Dos:A lw ays calculate exactly h ow m uch finished concrete is requ ired for the job to do and asce rtainhow m uch cem en t sand , coarse aggregate and w ater w ill be required

Why?E ven a go od gu ess can go w ron g. W hile g ue ssing the am ou nt of m aterial req uired it canhappen that you order to m uch, resulting into un ne cessary expenses. It m ight also h appe n thatyou order too less and organizing im m ediately the rem aining m aterial m ight proof to be difficultor eve n im possible, resulting into un necessary expenses and loss o f quality.

Dos:U se alw ays-clean sand and aggreg ates for concrete.

Why?C ontam inated sand and aggregate (e.g. roots, leaves, plastic parts, saw dust, an im al andhu m an e xcreta etc. w ill no t bind w ith cem en t, he nce is w eakening the concreter. A lso sandand aggregate w ith high percentage of clay or silt w ill w eaken the concrete, because the clayor silt contains too m any fine s that needs to b e cove red by cem ent for proper bind ing, hence,the concrete b ecom es w eak.


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Dos:A lw ays use fresh and lum p free cem en t for con crete

Why?O ld cem en t is loo sing its stren gth prop erty. E .g. cem en t that has b ee n stored for abo ut 6m on ths is gaining 30 % less stren gth than fresh ce m en t. For go od con crete w ork, stren gth isim portan t as it influence s the overall building quality.

Dos:A lw ays m ix the dry ing red ien ts (sand & cem en t) tog ethe r be fore ad ding w ater.

Why?W et sand particles have the ten de ncy to stick toge ther and are the refore hinde ring that cem entcan cover them . Th is results in an un-uniform m ix that is reducing the concrete quality, becau seeach sand and aggreg ate p article should ideally be fully covered w ith cem ent.Furthe r, add ing w ater tog ether w ith sand , aggregate and cem en t in on e go m akes m ixing theco ncrete extrem ely difficu lt for the laborers.

Dos:A lw ays protect the con crete-m ixing place from w ind , rain and sunshine .

Why?W ind an d su nshine is en training the w ater from the concrete and is acce lerating the harde ningprocess b efore it is being used. Th is is m akes the concrete u seless for any purpose. R ain isadding w ater and the concrete is becom ing too w et, resulting in a w eak final strength.

Dogs will contaminate concrete raw material, therefore proper protection is required


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DosU se the con crete m ix w ithin a m axim um of 1 h r. after w et m ixing and do never retem pe ringby m ixing in additional w ater

Why?In concrete that is o lder than 1 hr., the hydration process o f the cem ent has started and re-m ixing it is destroying the bo nd be tw ee n cem ent and sand /agg reg ates. This bon d cann ot reg ainstrength again by sim ply adding fresh w ater to the concrete.

Dos:U se alw ays-prop er qu antity m easuring boxes.

Why?U sing em pty cem en t bags, or other m eans does not alw ays ensure that the correct am ou ntof raw m aterial is being added. Th is inaccuracy could lead into a leaner or riche r m ix thandesigned, either reducing the concrete quality or adding e xtra co sts.

Dos:A lw ays m ake a final check of the form w ork before placing the concrete into the form .

Why?D uring placing of the reinforcem en t som e su pp orting po ols or bracing m igh t have be endislocated. If now concrete is pored into the fram ew ork, side shuttering or even slab shutteringm ight collapse . This is the w orst-case scenario, but unfortunately it still hap pens too often,som etim es even killing pe op le.

DontsD o n ot m ake con crete w ork if the ou tside tem pe rature is crossing 40 de gree C elsius.

Why?Th e direct sunshine tem pe rature at 40 de gree C elsius is nearly 50 d eg ree C elsius . H ence,the w ater evaporation of the freshly p lace d concrete w ill happen im m ediately, causing seriousshrinkag e cracks and hindering a p roper and controlled hardening of the concrete. Th is w illfinally se riously w eake n the concrete w ork quality.

H ow eve r, if it is u navoidab le to stop concreting w ork, then the follow ing precau tions can be

taken:n C oo ling dow n the aggreg ates by w ater sprinklingn P roviding a shade at the casting siden P lacing im m ediately plastic on the casted concrete

DontsD o n ot store the steel bars direct on the ground.

Why?The stee l bars m igh t ge t dirty and covered w ith m ud . If the m ud w ill no t be prop erly w ashedaw ay before concrete casting, the b inding o f the steel bar w ith the concrete is reduced,

resu lting in a w eak structure.


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DontsD o not clean the rust of the steel bars.

Why?A n alkaline environm ent, cem ent, surrounds the steel bars. Th e alkalinity o f the cem ent w illclean the rust in a very short tim e, provided no air is acce ssing the steel bars.

2.11 Form work M ost structural concrete is m ade by casting concrete into previou sly m ade boxes that are

called form s o r shuttering. U sually w all, colum n, beam and slab form s are built by joiningw oode n b oards e dge o n e dge. S om etim es p lyw oo d m ay be nailed on since it is tigh ter andm ore w rap resistant. In certain cases m etal form s are use d, e.g . w he n a large nu m be r of equ alstructural m em be rs (pre-cast elem en ts) have to b e e rected or w he n the parts shou ld b e ve ryexact in m easurem ents.

Th e m ost suitable m aterial for form w ork is w ood, in particu lar boards, rails, batten and planks.A ll this tim ber is available in various quality an d d im ension. H ardw ood should n ot be u sed forparts w here n ailing is necessary. B oards of less q uality an d boards of rough surface d o n ot lastvery long as shuttering. U sing plastic o r m etal sheets can extend the reuse.

Steel bars properly stored atconstruction site.

A ll form w ork m aterial (planks, boards, steel etc.) and e lem ents form w ork (m oulds) aresprinkled w ith w ater before placing concrete. A fter striking o r dism an tling, the form w ork is

cleaned and eve ntually o iled as w ell as properly stored and protected from sun and rain. Th isw ill gu arantee the use of m any tim es.


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Fo rm w ork for pre-cast products like cover slabs, fence posts, w ell and cu lvert rings, andelem en t form w ork for standard structures like stand po sts sh ou ld be m ade of quality tim be ror steel. Th e u se of G I sheets as additional reinforcem ent for tim ber form w ork is very su itab lebecause nailing of sideboards or batten is still possible

2.12 Removal of the formsForm s shou ld be left in place un til the con crete has harde ne d e no ug h to ho ld its ow n w eigh tand any othe r w eigh t it m ay be carrying . Th e su rface m ust be hard e no ug h to rem ain u ninjuredand un m arked w hen care is used in stripp ing the form s.

U nder ordinary circum stances, form s for various types for construction b e rem ove d afterintervals as follow s:

Side forms on beams, lintels, walls, columns 1 to 2 days

Slabs, lintels, beamsClear span 3 m and belowCle

Basic Construction Training Manual (Civil)

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